A female police officer has been left with a potentially life-changing injury in a central London attack which also saw her colleague stabbed in the neck.
The stabbing near Leicester Square at 06:00 BST is not related to the Queen’s death or terror-related, police say.
London Mayor Sadiq Khan branded the incident as “utterly appalling” at a “momentous time for our country”.
A man in his 20s has been arrested on suspicion of grievous bodily harm and assaulting an emergency worker.
The female officer was stabbed in the arm before her colleague ran after the “frenzied” suspect after which a tussle ensued, Met Police Commissioner Sir Mark Rowley said.
The male officer was “very seriously injured” after being stabbed three times in the neck and once in the chest but should make a full recovery, he added.
Other colleagues joined and fired a Taser at the suspect during the “violent struggle” on Great Windmill Street, near Shaftesbury Avenue. He was subdued and then arrested, Sir Mark said.
He has since been discharged from hospital into police custody.
The officers’ families have been told about the “very concerning” attack, Scotland Yard said.
Praising the officers’ bravery, Sir Mark said: “It’s a reminder to me that with all the calls for reforming the Metropolitan Police, which are absolutely necessary, we should never forget that we’ve got thousands of dedicated men and women going out every day who are prepared to be brave for Londoners.”
The stabbing took place close to Haymarket, between Leicester Square and Piccadilly Circus, which is home to many of London’s theatres and Chinatown.
Overnight, two other officers were injured, including one who was driven into by a car in south London, according to London’s mayor.
Khan said: “These brave officers were doing their duty and assisting the public at this momentous time for our country.
“My thoughts and prayers are with them, their loved ones and police colleagues following this disgraceful attack.”